The present invention relates generally to a positioning device, and specifically to a positioning table or fixture used for robotic automated systems. Rotary tables or fixtures carrying work objects are often used in robotic systems. An operator places the work object on one side in one workstation while a robot processes another work object on the opposing side of the fixture. The fixture then rotates in a reciprocating motion to reverse the two parts.
In order to accomplish the high-speed station exchange, the positioning device must be able to accelerate the table or fixture quickly and decelerate it quickly. If the fixture is traveling at full speed near the end of the exchange, it will have difficulty stopping and may cause damage to the system and the need for frequent repair or replacement of parts.
Other previous designs have used a flow torque control device that includes a rack and pinion driven by a singular air hydraulic cylinder. The pinion in these designs is small and does not produce much torque.
Another prior art design involves high-speed tables that use an electric motor. The problem with this type of table, however, is that the motor must be oversized to accommodate the fast acceleration and deceleration required for the table.
Additionally some prior art devices, such as that disclosed in U.S. Pat. No. 5,704,601 to Mangelsen, et al., have solved the above stated problems through the use of a singular cylinder assembly including a cylinder, a piston, and a rod carried by the piston. While the system of the ""601 patent is remarkable in its solution to the above stated problems, the singular cylinder design required inertia be relied upon in order to effectuate the proper rotation of the position device. The positioning device contained a no power point, or a point at which the cylinder was incapable of exerting force upon the positioning table or fixture. It is therefore desirable to provide a positioning device that is capable of exerting force, and thereby control, over the positioning table or fixture at all points of its rotation.
There is therefore a need in the art for a reciprocating high speed positioning device which can quickly accelerate and decelerate without putting stress on the parts of the system.
It is therefore a primary objective of the present invention to provide a reciprocating high speed positioning device which can overcome the problems found in the prior art.
Another objective of the present invention is to provide a reciprocating high-speed positioning device that is powerful, yet not oversized.
A further objective of the present invention is to provide a reciprocating high-speed positioning device, which can accelerate and decelerate quickly without damaging the parts of the system.
A still further objective of the present invention is to provide a reciprocating high speed positioning device which is easy to use and economical to manufacture.
The means and method of accomplishing these and other objects will become apparent from the following description of the invention.
The forgoing objects may be achieved by reciprocating positioning device comprising a frame, a table or fixture, and a bearing assembly rotatably mounting the table or fixture to the frame for rotation about a table or fixture axis. The table or fixture axis can be horizontal, vertical, or at any particular angle that is convenient for the human or robot operator.
Dual cylinder assemblies are connected to the frame at an oblique angle with respect to each other. Each cylinder assembly includes a cylinder, a piston, and a rod carried by the piston. Each piston and rod are moveable within the respective cylinder between an extended and retracted position. Each rod is pivotally connected to the table or fixture at a pivot point spaced from the table or fixture axis. The table or fixture is rotatable from a first position wherein the first rod is in its extended position and the second rod in a partially retracted position to a second position wherein the second rod is in its extended position and the first rod in a partially retracted position.
The dual cylinder assembly allows for precise rotation of the table or fixture to any position between the first and second positions. The exact position of the table or fixture may be monitored through the use of a sensor, such as a digital encoder. The encoder provides an electrical pulse train that can be used to determine speed and direction of rotation. This allows for precise controlling of the exact table or fixture position and prevents any damage to parts of the system. Of course, it is to be understood that the procedure for rotating the table or fixture easily may be reversed and therefore the table or fixture may be rotated a full 180xc2x0 in the opposite direction. Therefore, the table or fixture has a complete 180xc2x0 range of motion.
A control means is connected to the dual cylinder assembly and to any sensors used so as to cause the table or fixture to move from its first position to any other desired position. The control means will extend or retract the appropriate rods as required to properly place the table or fixture in correct position.
Another feature of the invention includes an optional safety brake, which provides emergency stopping to the system. The emergency brake is automatically activated when the power system is off. The control means that powers the reciprocating turntable or fixture also provides the power to inactivate or activate the safety brake. The brake is mounted between the bearing assembly and the turntable or fixture and applies pressure, which prevents rotation of the reciprocating table or fixture assembly.